There are known cutting tools of metal-ceramic materials based on high-melting metals, which have a wear-resistant coating of heat-resistant compounds, such as carbides and nitrides, of high-melting metals, such as titanium and zirconium. Between the coating and the base material there is an unbroken intermediate layer of a pure metal, such as titanium or zirconium (cf. the thesis by I. A. Derevlyov "Issledovaniye rabotosposobnosti instrumenta s tonkimi pokrytiyami v usloviyakh preryvistogo rezaniya" ("Studies of Wear Resistance of Tools with Thin Coatings Under Discontinuous Cutting Conditions"), Moscow, 1978, pp. 65-68).
The continuous intermediate layer of a pure metal is 0.5 to 1 mu thick and serves as the interface between the coating and the base material. Such tools are extensively used in metal working. In the case of machining constructional materials, they display a wear resistance which is 2 to 3 times as high as that of hard-alloy tools without a wear-resistant coating. On the other hand, such tools are expensive and not readily available. There is known a method for the manufacture of cutting tools of high-speed steels and hard alloys, according to which condensation of plasma matter and ion bombardment are used in order to successively deposit an unbroken intermediate layer of a pure metal and a coating of heat-resistant compounds of high-melting metals on the base material (of. the collection of papers "Progressivnyie technologicheskyie protsessy v instrumentalnom proizvodstve" ("Advanced Methods of Tool Manufacture") ed. by M. F. Semko, D.Sc. (Tech.), Moscow, 1979, pp. 26-28). During the deposition of an unbroken intermediate layer and a coating, tools of high-speed steel are maintained at a temperature below 560.degree. C., while tools of hard alloys are maintained at 800.degree. C. The condensation rate is 40 to 150 .ANG./sec.
There are known cutting tools of ceramic materials and aluminum oxide-based metal-ceramic materials, which are used to cut steel and cast iron.
These tools are much cheaper than tools of hard alloy-based metal-ceramic materials, but their applications are limited by their physical drawbacks.
The basic disadvantages of such tools are a low resistance of their cutting edges to lateral flexure, and a high sensitivity to thermal shocks.
The low lateral flexure resistance is due to the presence of numerous defects, such as microcracks, pores, and interfaces between grains, in the surface layer of a tool. As a result, the tool is chipped off during cutting.
The above disadvantages could be eliminated by coating such tools with a wear-resistant material, but cutting tools of an aluminum oxide-based metal-ceramic material with a wear-resistant coating are yet unknown.